1. Field of the Invention:
This invention relates to flash lighting units for photographic cameras, and more particularly to an improved flash lamp firing circuit for securing the reliability of operation of a flash lamp in a manner not to fire the lamp before the camera is made ready for flash photography regardless of the striking of the lamp.
2. Description of the Prior Art:
It is known to provide a flash lamp firing circuit having means capable of switching the associated camera from a day-light exposure range to a flash exposure range in automatic response to the attainment of the voltage of a storage capacitor to a satisfactory lamp firing level. As far as is known, however, the conventional types of circuits as such are characterized by the lack of means for preventing the lamp from being fired when the striking of the lamp is caused to occur before the voltage of the storage capacitor reaches the satisfactory firing level, though it is above a critical breakdown voltage level of the lamp. It has often happened that the camera is caused to operate in the day-light exposure range with the flash lighting unit being effective. It is, therefore, resulted that when the effective exposure time is relatively shorter, the magnitude of the exposure will be varied in different regions of an image. In the case of longer exposure times, the photographic film is over-exposed by an amount proportional to the total energy of flash light produced from the fired lamp.